1. Field of the Invention
The present invention relates to a measurement method and measurement apparatus configured to measure a spectroscopic characteristic inside a scattering medium (specimen).
2. Description of the Related Art
A conventional measurement apparatus as used for the optical mammography can create an image of a spatial distribution of a spectroscopic characteristic or metabolism of a biological tissue by measuring a spectroscopic characteristic or an attenuation characteristic in the biological tissue. The spectroscopic characteristic includes an absorption (spectroscopic) characteristic and a scattering (spectroscopic) characteristic, which will be also referred as an absorption-scattering characteristic in this application. Diffuse optical tomography (“DOT”) is known as a conventional measurement method.
DOT introduces the near infrared light into a scattering medium, and detects the diffused light, as disclosed in Japanese Patent Laid-Open No. (“JP”) 2005-331292. JP 2005-331292 assumes an internal distribution of a spectroscopic characteristic, and uses an algorithm that changes the assumption or reconstructs the assumed internal distribution based on a measurement result.
Other prior art include U.S. Pat. Nos. 6,738,653, 5,840,023, 6,957,096, and Lihong V. Wang, “Mechanism of Ultrasonic Modulation of Multiply Scattered Coherent Light: An Analytical Model,” Phys. Rev. Lett., vol. 87, No. 4, 2001 and Gang Yao and Lihong Wang, “Signal dependence and noise source in ultrasound-modulated optical tomography,” Appl. Opt. vol. 43, No. 6, 2004.
The image reconstruction method described in JP 2005-331292 requires complex, huge, and time-consuming calculations for the internal distribution, and is less likely to converge to an optimal solution quickly. A finer resolution is required for DOT measurement result.